Siena (unknown date or place of birth) is a fictional character from the Disney Channel series, Hannah Montana. She is portrayed by Tammin Sursok. Siena is a extremely rich bikini model. She is Jackson's current girlfriend. She and Jackson met her at the beginning of Season 4, and grew very close to her. She learned Miley's secret before it was publicly revealed, and remained with Jackson though he wasn't rich or famous.

Jackson meets through her rude cousin who happens to be the Stewart's neighbour in the season four premier episode, Sweet Home Hannah Montana. Siena is Jackson's unofficial girlfriend, though the romantic feelings are mutual. Siena is Jackson's longest running girlfriend.
As of California Screamin they have been together for three weeks and have kissed each other. Rico is shocked by the relationship, wondering how a girl as hot as Siena could ever be with a guy like Jackson. He was so shocked when they kissed, that he fell out of a tree. Due to Siena being away doing a photo shoot in Peru, Jackson was away from her for a week and decided to help Rico out in returns for a $2,000 check which he spent on a ticket to Peru.

Trivia

Siena is Jackson's first "serious" girl

Siena, unlike her boyfriend, is more sophisticated and beautiful, but despite the differences between her and Jackson, Siena is truly in love with him.